1. Field of the Invention
This invention relates to protecting the occupants of a burning building from exposure to visible smoke and noxious fumes. It further relates to preventing the spread of smoke through the upper floors of a burning building. It particularly relates to controlling the lateral and vertical passage of smoke and air through ducts, ventilation passages, and air-conditioning conduits of burning buildings.
2. Review of the Prior Art
Because fire retardants are combustion inhibitors which promote smoldering rather than burning and further because fire retardants are presently used widely for treating wood, furniture materials, draperies, and the like, there is an increasing tendency to produce killer gases, such as carbon monoxide, when fires occur in homes and large buildings such as offices, apartment buildings, hotels, hospitals, and the like. Carbon monoxide is particularly dangerous because its affinity for human blood is 300 times greater than that of oxygen so that it displaces oxygen very rapidly from the blood. In consequence, an atmosphere containing 0.1% CO causes a severe headache and nausea within an hour and can cause coma within 2 hours and death within 4 hours.
Smoke is herein defined to include the invisible gaseous products of early combustion of burning organic materials, particularly including carbon monoxide, as well as the visibility-obscuring gaseous suspension of submicroscopic particles which is commonly recognized. Smoke herein further includes any chemical fumes and noxious gases such as are produced by chemical reactions or spillage of chemicals from tank cars or storage tanks. Smoke herein additionally includes heated but uncontaminated air at a temperature too high for life to endure. As so defined, smoke kills four out of five fire victims by asphyxiation before contact with heat or flames.
The generation of smoke, moreover, is but a part of the problem of protecting the occupants of a burning building; its rapid lateral and vertical transmission through modern ventilation, heating, and air-conditioning systems causes many fatalities far in advance of the fire or even after the fire has been localized or substantially extinguished.
When a fire begins in the vicinity of the furnace in a large building, various steel fire dampers, installed in the ducts in front of and behind the furnace and generally conforming to NFPA No. 252, "Standard Method of Fire Tests of Door Assemblies," close automatically. Such dampers generally have an interlocking blade design and are fitted with a spring catch requiring manual resetting whenever fully closed. They posses at least a 11/2 hour National Fire Protection Association (NFPA) rating and are closed when a fusible link separates.
Fires can also begin in an upper floor of a large building, particularly in storage rooms containing, for example, paints, solvents, and the like or mattresses, bedding, and the like. Because flames can not reach beyond twenty feet within a duct, fire dampers are ordinarily placed in the vicinity of the furnace but not throughout the building. Smoke from fires originating in an upper room can thus travel both laterally and vertically with relatively little hindrance through the duct system, particularly if the room is provided with a register or a diffuser and the duct system is under relatively low pressure. If the duct system is under relatively high pressure, however, the smoke may instead diffuse throughout the floor on which the room is located.
According to National Fire Protection Association Pamphlet 90A, a smoke damper is a damper arranged for automatically interrupting air flow through a part of an air duct system so as to restrict passage of smoke, but it need not meet all the requirements of a fire damper.
Smoke dampers are commercially available. One form uses interlinked steel louvers which descends when a fusible link separates, but such a damper is not and can not be completely sealed at its edges so that it merelly delays and minimizes the movement of smoke through ducts. Consequently, there is a need for a smoke blocking device which can completely seal a duct and thereby prevent smoke from spreading laterally and vertically through a burning building or which can snuff a fire by preventing access of fresh air thereto through a duct.